Frog Deaths: “A Complicated Mystery”: What Kills Sydney’s Frogs

dr Jodi Rowley.

dr Jodi Rowley.Recognition:Stuart Humphreys

Seeing a dead frog is rare – they are secretive, their bodies decompose and are often snatched by predators.

But as autumn turned to winter last year and Rowley heard hundreds of reports of dead frogs across Australia, she quickly began trying to figure out what was killing them, an effort that has rolled into this year as a second wave arrives.

A possible reason for the spike in deaths could be a record year of rainfall caused by the La Niña cycle. Like humans, frogs’ immune systems are weakened in cooler weather, while at the same time the chytrid fungus thrives in cooler, wetter conditions.

Having the fungus in their system isn’t necessarily a death sentence for most frog species, but they can die “quite quickly” if the fungus builds up to a level where their skin can’t breathe and drink, Rowley said.

“These wet summers and wet winters that we’re having are most likely pretty bad news for frogs. We’re really concerned about frogs in Sydney. We are very lucky to have the frogs that we have. We don’t want to lose anymore.”

A new study from James Cook University, published Thursday, suggests that variations in the microbiomes — the bacteria, fungi and other microorganisms found on the frogs — could play a key role. dr Donald McKnight, co-author of the study, said the research could have implications for how conservationists mitigate the threat posed by the chytrid fungus.

“It may be that the presence of the fungus that causes chytridiomycosis actually allows antifungal bacteria to thrive…or possibly only frogs with high levels of antifungal bacteria can survive a high load of infection,” he said.

Karrie Rose of the Taronga Australian Registry of Wildlife, who worked with Rowley on the frog deaths, said the recent death event is an example of the impact of widespread ecological changes on wildlife health.

“We are now seeing patterns of disease occurrence in wildlife after the floods that are very similar to what we saw just after the bushfires,” she said.

“We’ve had pandemics in humans, so it’s not unexpected that we’ll see similar events in wildlife… they’re just coming more frequently and spreading more than we’ve ever seen in the past.”

If you see a sick or dead frog you can email details and photos to the Frog ID project:

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Chris Barrese

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